Timber Harvest Sustainability Calculator

The Allowable Annual Cut is the maximum volume of timber that can be harvested from a forest area each year without depleting the resource over time. It is based on the annual growth increment of the stand, the harvestable area (total area minus protected zones), and the chosen harvest method's intensity. Keeping harvest below the AAC ensures the forest can regenerate and remain productive indefinitely.

The sustainability score (0–100) combines three factors: how well the planned harvest aligns with the growth rate (harvest-to-growth ratio), the proportion of area protected for conservation, and the age maturity of the stand relative to its rotation period. A score above 70 is considered sustainable, 40–70 is marginal, and below 40 indicates over-harvesting risk.

Carbon stock is estimated by multiplying the standing volume (m³/ha) by wood basic density (t/m³) to get dry biomass, then multiplying by the carbon fraction (default 0.50 per IPCC Tier 1 guidelines), and finally by the CO₂ equivalent factor (3.667). This gives above-ground carbon stock in tCO₂e per hectare, scaled to the total harvestable area.

The rotation period is the time between successive harvests on the same area, allowing the stand to regenerate to a productive state. It depends on species growth rates, desired timber size, and management objectives. Fast-growing plantation species like loblolly pine may have rotations of 25–40 years, while slower-growing species like Douglas fir or red cedar typically require 60–120 years.

Selection cutting (20–35% removal) is the most ecologically sustainable option, maintaining continuous canopy cover and high biodiversity. Thinning (10–20%) is used for stand improvement rather than full harvesting. Shelterwood systems (50–70%) gradually open the canopy to encourage regeneration. Clearcutting (80–95%) maximises short-term yield but requires careful planning to avoid soil erosion, habitat loss, and carbon release.

Reserved areas serve as biodiversity refuges, riparian buffers, and old-growth conservation zones. Most sustainable forestry standards (FSC, PEFC, SFI) require that a portion of the managed landscape be excluded from harvesting. Retaining 15–20% or more as protected forest significantly improves the sustainability score and supports long-term ecosystem health.

Basal area (m²/ha) measures the density of trees in a stand and is a key indicator of stocking level. Well-stocked productive stands typically have basal areas of 25–50 m²/ha for most temperate species. Very high basal areas (>60 m²/ha) may indicate over-stocking and competition stress, while low values (<15 m²/ha) suggest under-stocking. Harvest planning uses basal area to determine how much thinning or removal is appropriate.

This calculator provides a solid first-order estimate of carbon stocks and annual sequestration based on IPCC Tier 1 methodology, making it useful for preliminary carbon project scoping. For verified carbon credits (under standards like Verra VCS or Gold Standard), you would need site-specific forest inventory data, third-party verification, and a full carbon accounting methodology that includes below-ground biomass, dead wood, and soil carbon pools.